The present invention relates to a steam generator, more particularly intended for use in pressurized water nuclear reactors and provided with a dynamic bleeding or draining device facilitating the removal of the water separated from the steam in the generator dryer.
FIG. 1 shows a steam generator of the type presently used in pressurized water reactors. The generator 1 comprises a cylindrical tight enclosure 2 surrounding a group of U-tubes 4 in which circulates the primary liquid. The lower part of the tubes 4 is fixed to a tube plate 6 and these tubes are connected on the one hand to an intake chamber 8 through which enters the hot primary fluid and on the other hand to a discharge chamber 10 permitting the cooled primary liquid to return to the reactor. A cylindrical envelope 12 surrounds the group of tubes 4 and defines with the inner wall of enclosure 2 an annular passage 14 for the circulation of the secondary liquid. The latter reaches the generator through a pipe 16 and then descends in annular passage 14 to tube plate 6, enters through a passage made in between plate 6 and the lower edge of envelope 12 and then rises along tubes 4, where it vaporizes on contact with the hot primary fluid. In the upper part of cylindrical envelope 12 there is a cover 18 in which are provided a plurality of passages such as 20, each being provided with a device for separating by centrifuging the water entrained with the steam. On leaving device 22 the steam still contains a certain amount of water, which must be eliminated before the steam reaches the turbine of the alternator. For this purpose the upper part of the generator is provided with a dryer 24, generally having passages provided with baffles on which the water drops are deposited and drop into the generator through discharge pipes 26. The generator shown in FIG. 1 has two superimposed dryers 24, 25 connected to the lower part of the generator by discharge pipes 26, 27 respectively. It is also possible to see a central collector 28, whose action completes that of discharge pipes 26, 27. FIG. 1 also shows that the free surface of the secondary liquid outside envelope 12 reaches the level of centrifuging device 22 and that the free ends of pipes 26, 27 and collector 28 are below this surface. In view of the fact that the dryers 24, 25 lead to a pressure drop in the steam circuit, a water level called the "clearance level" is established in the discharge pipes, so that the difference in level between the free surface of the liquid in the discharge pipes and within the enclosure 2 approximately corresponds to the pressure drop through dryers 24, 25. For satisfactory operation of the system, it is also indispensable that the water level in the discharge pipes be below the level of the lower part of dryers 24, 25. The need to maintain a minimum clearance level in the discharge pipes consequently leads to large overall dimensions level with the steam generators.